Lock stitch sewing machine having a rotatable shuttle

ABSTRACT

A lock stitch sewing machine, comprises a sewing machine housing having a bed plate with an opening therethrough, with a needle reciprocating on one side of the opening and a rotatably mounted shuttle on said housing on the opposite side of the opening for cooperation with the sewing needle. The shuttle includes a bobbin case with a shuttle rotatable in said case which has a thread loop pickup point. A supply of thread is located in the case on a spool and a case carrier having a catch shoulder for engaging the thread and also having a carrier stop is rotatable in the bobbin case for limited rotation between defined limits. The limits are defined by stop surfaces on a stop fixture. The stop fixture comprises a spring having a free end portion which is disposed in a plane parallel to the rotation plane of the shuttle and the transversely extending stop surface defining a thread guide portion for a thread guide edge which extends obliquely to the pull off path of the needle thread loop. The thread guide edge and a radially extending stop member edge of the carrier stop diverge from the straight interior stop surface in a direction opposite to the pull off direction of the needle thread loop.

United States Patent [191 Gustmann et al.

[451 Nov. 25, 1975 Ramstein-Miesenbach, both of Germany [73] Assignee: Pfafi Industriemaschinen GmbH,

Germany 22 Filed: Nov. 18, 1974 211 Appl. No.: 524,863

[30] Foreign Application Priority Data Dec. 11, 1973 Germany 7343899[U] [52] U.S. Cl 112/181; 112/228 [51] Int. C1. D05B 57/14 [58] Field of Search 112/181, 228, 231

[56] References Cited UNITED STATES PATENTS 2,352,598 7/1944 Billington 112/181 X 2,394,369 2/1946 Colegrove 112/228 2,446,150 7/1948 Wood 112/228 2,873,706 2/1959 Tateishi 112/181 2,990,794 7/1961 Ketterer 112/228 3,145,673 8/1964 Meloy 112/181 3,199,480 8/1965 Covert et al. 112/231 FOREIGN PATENTS OR APPLICATIONS 1,166,541 6/1958 France 112/181 1,061,662 3/1967 United Kingdom 112/181 Primary ExaminerAlfred R. Guest Attorney, Agent, or FirmMcGlew and Tuttle s7 ABSTRACT A lock stitch sewing machine, comprises a sewing machine housing having a bed plate with an opening therethrough, with a needle reciprocating on one side of the opening and a rotatably mounted shuttle on said housing on the opposite side of the opening for cooperation with the sewing needle. The shuttle includes a bobbin case with a shuttle rotatable in said case which has a thread loop pickup point. A supply of thread is located in the case on a spool and a case carrier having a catch shoulder for engaging the thread and also having a carrier stop is rotatable in the bobbin case for limited rotation between defined limits. The limits are defined by stop surfaces on a stop fixture. The stop fixture comprises a spring having a free end portion which is disposed in a plane parallel to the rotation plane of the shuttle and the transversely extending stop surface defining a thread guide portion for a thread guide edgewhich extends obliquely to the pull off path of the needle thread loop. The thread guide edge and a radially extending stop member edge of the carrier stop diverge from the straight interior stop surface in a direction opposite to the pull off direction of the needle thread'loop.

4 Claims, 5 Drawing Figures Patent Nov. 25, 1975 SheetlofZ 3,921,551

US. Patent Nov. 25, 1975 Sheet20f2 3,921,551

LOCK STITCH SEWING MACHINE HAVING A ROTATABLE SHUTTLE FIELD AND BACKGROUND OF THE INVENTION This invention relates in general to the construction of sewing machines and, in particular, to a new and useful lock stitch sewing machine having a rotatable shuttle with a carrier stop member which moves relative to the shuttle between limits defined by a stop fixture. In order to permit the clearing of passage gaps between the stop member and the stop surfaces necessary for guiding the needle thread loop around the bobbin case carrier.

DESCRIPTION OF THE PRIOR ART Lock stitches are formed in a sewing machine by passing the needle thread downwardly through the fabric with the needle and enlarging the thread loop formed by engaging it with a point of a shuttle and guid ing it around the'entire bobbin case carrier which encloses-a thread supply so that the needle thread and the shuttle thread become interlaced with each other. During this operation, the bobbin case carrier accommodates the supply thread which, in most cases, is recelved on a bobbin which must be secured by a stop member against rotation along with the shuttle. During the guiding of the needle thread loop around the bobbin case carrier, in which the supply of thread is enclosed, the needle thread loop is picked up by the point of the rotating shuttle and passes into a recess formed by the interruption of the track rib of the bobbin case carrier and it is further guided around the case carrier with one branch of the loop in front of, and one branch of the loop behind, the carrier. As the shuttle reaches the cast-off position of the needle thread loop, the usual take-up lever of the sewing machine starts to pull the enlarged needle thread loop upwardly to terminate the stitch formation by tightening the interlacement in the fabric of the lower thread and the needle thread. Since the stop member of the bobbin case carrier is entrained in the direction of rotation of the shuttle, due to the friction between the case carrier and the shuttle which occurs during the rotation, the stop member of the case carrier is entrained in the direction of rotation of the shuttle and, therefore, applies against one of the stop surfaces of the stop fixture. Thereafter, the gap between the stop member and thestop surface, located on the side opposite the direction of rotation of the shuttle, becomes cleared for the passage of the thread. However, to complete the guidance of the needle thread loop around the bobbin case carrier, which carries the supply of the lower thread, it is necessary to open the passage gap between the stop member and the stop surface in the direction of rotation of the shuttle.

In sewing machines which operate only at low speeds, this is done by turning the bobbin case carrier with the bobbin case merely by the pulling force exerted on the thread by the take-up lever during the pulling up of the needle thread loop. If higher speeds are provided, the opening of one of the thread passage gaps must be effected by means of a special control device.

In known sewing machines, the opening of the thread passage gap is effected so that an eccentric-driven finger applies against a shoulder of the bobbin case carrier and turns the bobbin case carrier in the direction opposite to the direction of rotation of the shuttle. The stop member of the bobbin case carrier is therefore thrown against a stop surface of a groove which, in general, is provided in the stitch plate or in a stop fixture. Thus, it suffers a rebound which becomes stronger with increased speed. An undesirable: metallic noise is thereby produced, and the component parts are considerably heated up. In addition, if the speed is increased, natural oscillations of the bobbin case carrier are generated which are not controllable and have an unfavorable effect on the sewing operation. What is more, in some cases, the thread between the stop member of the bobbin case carrier and the stop surface of the stop fixture is hammered through.

In a known device, the drive eccentric for the thread passage opener ismounted on the shuttle shaft and the opener is securedv against rotation along with the shuttle shaft by means of a slide which is rotatably mounted in the shuttle support and projects into a slide guide of the opener. In this device, the lower thread case is turned once at each revolution of the shuttle. Such an arrangement has the advantage that only a relatively small stroke of the thread passage opener is required and, also, the finger of the opener is accelerated largely in accordance with the requirement of a well-timed .clearing of the thread passage gap and a subsequent relasing of the shoulder. However, the frequency of the opening movements does not permit high speeds of the machine since the rebound effect caused by the impingement of the stop member upon the second stop surface of the stop fixture increases rapidly with the speed. In order to reduce the rebound effect, it has been proposed in such a device, to provide the finger of the thread passageopener with a flat spring intended to cause the finger to turn the bobbin case carrier by slightly applying against the shoulder of the latter. This measure also proved unsuited for high speeds because of the frequency of the opening movements.

Since for operational reasons, a lock stitch shuttle generally revolves two times during the formation of a single stitch, only every second revolution of the bobbin case carrier is needed as an effective movement for the opening of the thread passage. In order to obtain the turning movement of the bobbin case only once at each stitch formation, in machines which require two revolutions of the shuttle, devices have been provided in which the drive eccentric is mounted on a shaft which rotates at the same speed as the needle bar shaft. In such a design, the motion of the eccentric is transmitted to the thread passage opener by means of a lever arm which is biased into contact with the eccentric. A substantial drawback of such devices is that, at high rates of stitch formation, which is required in the sewing industry at the present time, a reliable contact between the lever arm and the drive eccentric is not ensured.

There are also known devices for clearing the thread passage gap once during each stitch formation. These comprise a thread passage opener driven by a force closure. They work in a satisfactory manner, but the thread passage opener must be controlled along a special track of movement. This, of course, entails considerable constructional expenses.

In the view of the drawbacks. of the prior art, it would be advantageous to omit the device for opening the thread passage gap or the device for controlling the opening movement of the bobbin case carrier altogether. To this end, it has been proposed to pivot a spring loaded two armed holder on the bobbin case carrier and to use one of the holder arms to project bepermitting the holder to yield. However, in this device,

the relatively big mass of the holder has the same undesirable effect as devices for controlling the opening movements of the bobbin case carrier which have been mentioned before.

SUMMARY OF THE INVENTION This invention is directed to a device in which the stop element for the bobbin case carrier is movable and has a mass substantially reduced relative to the bobbin case carrier which encloses the bobbin case and the lower thread bobbin and it is designed so that the gap between the element and the stop member of the bobbin case carrier for the thread passage can be opened by the element itself without the necessity of turning the bobbin case carrier. For this purpose, the invention provides a spring stop which is mounted on a stop fixture and which has a free end movable parallel to the plane-of rotation of the shuttle and which includes a stop surface disposed in the direction of rotation of the shuttle as well as a thread guide portion having a thread guide edge extending obliquely to the pull-off path of the needle thread loop and in a direction such that the guide edge and the opposed lateral edge of the stop member diverge from the stop surface in the direction opposite to the pull-off direction of the needle loop.

In order that the guidance of the loop around the carrier is not hindered, the obliquely extending portion of the spring conforms to the shape of the stop member which is curved toward the needle. As a security against distortion, the spring comprises an intermediate portion which is guided in a groove of the stop fixture and which extends parallel to the plane of rotation of the shuttle. In order to limit the spring motion, the free tively movable in respect to the shuttle and which contains a stop member which is cooperable with a fixed stop of a stop fixture in order to permit the clearing of passage gaps between the stop member and the stop surfaces which are necessary for guiding the needle thread loop around the bobbin case carrier which encloses the bobbin case and the shuttle thread supply and wherein, the stop fixture comprises a spring which has a thread guiding portion which extends obliquely in respect to the carrier stop member such that the guide edge of the spring and the opposed lateral edge of the stop member diverge from the stop surface of the spring in the direction opposite to the pull-off direction of the needle thread loop.

A further object-of the invention is to provide a sewing machine which is simple in design, rugged in con- 4 ing advantages and specific objects attained by its uses. reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a partial side elevational view of a sewing machine having a shuttle with a stop fixture for the bobbin case carrier mounted on the bed plate in accordance with the invention;

FIG. 2 is an enlarged sectional view taken along the line IIII of FIG. 1;

FIG. 3 is a partial top plane view of the shuttle and the stop fixture for the bobbin case carrier;

FIG. 4 is a side elevational view of the stop fixture for the bobbin case carrier; and

FIG. 5 is an exploded perspective view, on a reduced scale, of the component parts of the rotatable shuttle.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings in particular, the invention embodied therein, comprises a sewing machine having a housing, generally designated 1, with a needle bar 2 carrying a needle 4 mounted for vertical reciprocating movement over a bed plate 7. Needle 4, during its reciprocation, guides a needle thread 3 through an opening of the bed plate 7 for cooperative engagement with a shuttle, generally designated 5. To form lock stitches (stitch No. 301), the needle 4 cooperates with shuttle 5 which is rotatable with shaft 9 mounted in a support 6 of bed plate 7 and is secured against axial displacement by an adjusting ring 8. Shuttle 5 is-provided with a point 10 which projects in the direction of rotation, as indicated by Arrow A in FIG. 2, and is intended to pick up the needle thread loop during its rotation. The thread loop comprises branches 11 and 12 and it is guided by the pick-up point around a bobbin case carrier 13 enclosing bobbin case 14 and shuttle thread 16 received on a bobbin 15.

As best seen in FIG. 5, bobbin case carrier 13 is formed with a bearing rib 17 which engages in a bearing track 18 of shuttle 5. Bearing rib 17 is interrupted at 19 so that a catch shoulder 20 is formed for the needle thread loop. A pin 21 is riveted into a bobbin case 14 which moves with bobbin case carrier 13. Bobbin case 14 can be locked in its working position on pin 21 by means of a hinged lid 22. A lower part 23 of the hinge engages a peripheral groove 24 provided on pin 21. Shuttle 5 also includes a strap member 25 which is screwed to the shuttle body by means of screws 26, and this strap member 25 overlaps the bearing rib 17 0f bobbin case carrier 13 which is received in bearing track 18.

Bobbin case carrier 13 is provided with a stop member, generally designated 27, which is formed as a radially outwardly extending part of carrier 13 and is curved generally toward needle 4. Stop member 27 includes a lateral edge 29 as well as a slopingedge 28 which provides a glide surface for the branch 1 1 of the needle thread loop, which, while the loop is guided around, extends infront of bobbin case 14.

Stop member 27 projects upwardly between two offset extensions 30 and 31 which, as shown in FIGS. 3 and 4, are part of a stop fixture 32 for the bobbin case carrier. Fixture 32 is secured to the underside of the bed plate 7. An extension 30 of stop fixture 32 has a beveled edge 33, conforming to, and cooperating with, the sloping edge 28 of stop member 27 and it serves as the stop surface of stop fixture 32 which limits the pivotal motion of bobbin case carrier 13 in the direction opposite to the direction of rotation, as indicated by the arrow A. The second stop surface of the stop fixture 32 which limits the pivotal motion of the bobbin case carrier 13 in the direction of rotation is a portion of the free end 35 of a leg spring or stop member 36 which is made of steel wire and is adapted to come into contact with the lateral edge 29 of stop member 27 at the loca' tion 34 shown in FIGS. 3 and 4.

Leg spring 36 is fixed by means of a screw 37 to the underside of stop fixture 32 at a location which is relatively remote from contact point 34. Spring 36 also includes two legs 38 and 39. In order to secure the position of spring leg 38, its extremity is bent at an angle and received in a bore 40 of stop fixture 32. Spring leg 39 extends from screw 37 first approximately parallel to leg 38 and then in a semicircle toward stop member 27 of carrier 13 while it follows the shape of the offset extensions 30 and 31. The semicircular portion of spring leg 39 is followed by a thread guide portion 41 which comprises an obliquely extending thread guide edge 42. Guide edge 42 extends obliquely to the lateral edge 29 of bobbin case carrier 13 and they diverge relative to each other in a direction opposite to the pull-off direction of the needle thread loop in order to facilitate the entrance of the needle thread loop into the passage gap between the lateral edge 29 of stop member 27 and the contact point 34 of spring 36 and also in order to ensure that the thread branch 12 applies early against thread guide edge 42 to thereby push thefree end 35 of leg 39 outwardly.

In order to ensure distortion-free motion of free spring end 35, thread guide portion 41 is followed by a straight intermediate portion 43 which extends parallel to the plane of rotation of the shuttle. In addition, the thread guide portion 41 and the straight intermediate portion 43 of spring leg 39 are shaped, as seen in lateral elevational view, so. as to approximately follow the curved shape of the stop member 27.

The extremity 44 of leg 39 of spring 36 is bent at an angle and projects into a bore 45 which is provided in stop fixture 32. Bore 45 is substantially larger than the wire diameter of spring 36. The straight intermediate portion 43 is guided in a groove 46 which is provided in stop member 32. Groove 46 opens into a bore 45. Consequently, leg 39 of spring 36 is guided so as to be movable within limits parallel to the plane of rotation of the shuttle and is secured against lateral deviation.

The operation of the device in forming a double lock stitch is as follows.

Needle 4 causes needle thread 3 to be passed through the fabric down below bed plate 7. During the first phase of the upstroke, needle 4 moves from its lowermost position, and the needle thread forms a loop which, at the rotation of shuttle 5 in the direction of arrow A, as shown in FIG. 2, is picked up by the shuttle point 10. During a further rotation of the shuttle, the needle thread loop is enlarged, and introduced into the interruption 19 of bearing rib 17 and held back by catch shoulder 20. With the catch shoulder 20 being considered as a point of division, the needle thread loop forms a front branch 11 and a rear branch 12. While the needle thread loop is guided around bobbin case carrier 13, which is enclosed within bobbin case 14 and around bobbin 15 and supply thread 16, front branch 11 passes in front of bobbin case carrier 13 and the rear branch 12 passes behind the bobbin case carrier 13 between the bobbin case carrier and the bottom of the shuttle.

Due to friction which occurs during the rotation of shuttle 5 between the shuttle and the bobbin case carrier l3, thecarrier is entrained in the direction of rotation of the arrow A, ,as shown in FIG. 2, and lateral edge 29 of stop member 27 applies against contact point 34 of leg spring 36. Thereby, a clearance is formed for the passage of front branch 11 of needle thread 3, as shown in FIG. 2, between the stop surface formed by the beveled edge 33 of extension 30 of stop fixture 32 which is located opposite to the direction of rotation and the sloping edge 28 of stop member 27.

After the shuttle 5 has reached the cast-off position for the needle. thread loop, the conventional take-up lever of the sewing machine begins to pull the enlarged needle thread loop upwardly. During this phase, the front branch 11 can pass without hindrance through the open thread passage gap between the beveled edge 33 and sloping edge 28 of stop member 27.

During the further pulling up of the needle thread loop by the take-up lever of the sewing machine, branch 12 applies against thread guide edge 42 which extends obliquely through the lateral edge 29 of stop member 27. Since the movable leg 39 of spring 36 has a substantially smaller mass than the bobbin case carrier 13, the bobbin case 14, bobbin 15 and supply thread 16, and because these parts are also exposed to a torque acting in the direction of rotation which is produced by friction between bearing rib l7 and bearing track 18, the thread does not push the parts in a direction against the rotation of sl'nuttle 5, but rather displaces spring leg 39 laterally ina direction parallel to the plane of rotation of the shuttle, thus clearing the passage gap between the lateral edge 29 of stop member 27 and the contact point 34 of spring end 35, so that branch 12 of the needle thread loop can pass therethrough. During this displacement of the spring leg 39, the straight intermediate portion 43 is guided in groove 46. The displacement is limited by spring extremity 44 which projects into bore 45.

As soon as branch 12 has passed through the thread passage gap between lateral edge 29 and contact point 34 of spring 36, the guidance of the needle thread loop around the bobbin case carrier 13 is fully completed. Subsequently, by means of the take-up lever, the stitch is firmly tightened, that is, the interlaced needle thread 3 and shuttle thread 16 are pulled into the fabric and drawn fast, whereupon, a new cycle of stitch formation may commence.

It is evident that with this device, it is not necessary to turn the bobbin case carrier 13 and the shuttle thread bobbin against the direction of rotation of the shuttle in order to open the thread passage gap between the stop member 27 of bobbin case carrier 13 and the second stop surface 34 of stop fixture 32. During the sewing operation, bobbin case carrier 13 remains motionless while both the front and rear branches of the needle thread loop pass through the gaps because, due to the substantially smaller mass of leg spring 36 relative to bobbin case carrier 13 and bobbin carrier 14, bobbin l5 and shuttle thread 16, the spring gives way under pressure on thread guide edge 42 exerted thereon while the needle thread loop is pulled upwardly by the take up lever and is displaced to the outside. In consequence, rebounds of the bobbin case carrier 13 and all the undesirable attendant phenomena are entirely avoided with such a device.

in sewing tests carried out on sewing machines equipped with the inventive device, another advantage was found, namely, that the tension of the needle thread can be considerably reduced. Due to this possible reduction of thread tension, the device is particularly suitable for zig-zag sewing machines. As is wellknown, a zig-zag seam must be formed at a very low needle thread tension in order to prevent a contraction of the material by the zig-zag stitches to a bead. While using a zig-zag sewing machine equipped with the device, in accordance with the invention. it is not necessary to change the tension values when switching from the formation of a straight seam to the formation of a zig-zag seam.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be un derstood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

l. A lock stitch sewing machine, comprising a housing having a bed plate with an opening therethrough, a reciprocated sewing needle mounted for reciprocation onsaid housing on one side of said bed plate opening, a shuttle rotatably mounted for rotation on said housing on the opposite side of said bed plate from said needle in position for cooperation with said needle, said shuttle including a bobbin case, a rotatable shuttle having a thread loop pick-up point, a thread supply in said case, a case carrier having a catch shoulder for engaging the thread and being rotatable relative to said shuttle within predetermined limits, a stop fixture mounted .on" said bed plate adjacent said shuttle, a spring on said stop fixture including a substantially straight interior portion extending substantially parallel to the plane of rotation of said shuttle and a thread guide edge connected to said straight interior portion and extending obliquely to the pull off path of said needle thread loop, said carrier having a carrier stop which comprises an outer circumferentially sloping edge portion and a radially extending stop member edge portion with a gap between said portions for the passage of a thread there through, said carrier stop radially extending stop member edge being engageable against the straight interior stop surface portion of said spring to permit displacement of said spring and clearing of the passage gap of said stop member for guiding the needle thread loop around the bobbbin case carrier. said thread guide edge extending obliquely to the pull-off path of the needle thread loop and diverging from a radially extending stop member edge of said carrier in a direction opposite to the pull-off direction of the needle thread loop.

2. A lock stitch sewing machine, according to claim 1, wherein said obliquely extending thread guide edge of said spring is conformable to the shape of said radially extending stop member edge which is curved toward said needle.

3. A lock stitch sewing machine, according to claim 1, wherein said spring comprises an intermediate portion, said stop fixture having a guide groove extending parallel to the plane of rotation of said shuttle providing a guide for said spring intermediate portion.

4. A lock stitch sewing machine, according to claim 3, 'wherein said intermediate portion has an end which is bent at an angle, said stop fixture having a bore into which said angled end of said intermediate portion extends and which bore is larger than the material thickness of said spring, said groove opening into said bore. 

1. A Lock stitch sewing machine, comprising a housing having a bed plate with an opening therethrough, a reciprocated sewing needle mounted for reciprocation on said housing on one side of said bed plate opening, a shuttle rotatably mounted for rotation on said housing on the opposite side of said bed plate from said needle in position for cooperation with said needle, said shuttle including a bobbin case, a rotatable shuttle having a thread loop pick-up point, a thread supply in said case, a case carrier having a catch shoulder for engaging the thread and being rotatable relative to said shuttle within predetermined limits, a stop fixture mounted on said bed plate adjacent said shuttle, a spring on said stop fixture including a substantially straight interior portion extending substantially parallel to the plane of rotation of said shuttle and a thread guide edge connected to said straight interior portion and extending obliquely to the pull off path of said needle thread loop, said carrier having a carrier stop which comprises an outer circumferentially sloping edge portion and a radially extending stop member edge portion with a gap between said portions for the passage of a thread therethrough, said carrier stop radially extending stop member edge being engageable against the straight interior stop surface portion of said spring to permit displacement of said spring and clearing of the passage gap of said stop member for guiding the needle thread loop around the bobbbin case carrier, said thread guide edge extending obliquely to the pull-off path of the needle thread loop and diverging from a radially extending stop member edge of said carrier in a direction opposite to the pull-off direction of the needle thread loop.
 2. A lock stitch sewing machine, according to claim 1, wherein said obliquely extending thread guide edge of said spring is conformable to the shape of said radially extending stop member edge which is curved toward said needle.
 3. A lock stitch sewing machine, according to claim 1, wherein said spring comprises an intermediate portion, said stop fixture having a guide groove extending parallel to the plane of rotation of said shuttle providing a guide for said spring intermediate portion.
 4. A lock stitch sewing machine, according to claim 3, wherein said intermediate portion has an end which is bent at an angle, said stop fixture having a bore into which said angled end of said intermediate portion extends and which bore is larger than the material thickness of said spring, said groove opening into said bore. 